Asset Allocation Drift Calculator
Deviation from target allocation triggering rebalance.
Calculate drift between current and target asset allocation to decide if rebalancing is needed. Enter equity to see drift percentage and rebalance flag.
What this tool does
Asset allocations drift over time as different assets perform differently. This calculator measures how far your current allocation has moved away from your target by comparing your current equity percentage to your target equity percentage. It then estimates the size of that deviation and indicates whether it has crossed your rebalance threshold—the point at which you might take action to realign your portfolio. The drift figure represents the percentage-point gap between where you are and where you intended to be. Results depend most heavily on the difference between current and target allocations, as well as the threshold you set. For example, if equities have outperformed and now represent a larger share of your portfolio than planned, drift will be positive. This calculation is for educational illustration and does not account for transaction costs, timing considerations, or other portfolio dynamics.
Enter Values
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Formula Used
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Calculations or display — let us know.
Disclaimer
Results are estimates for educational purposes only. They do not constitute financial advice. Consult a qualified professional before making financial decisions.
Target 60% equity / 40% bonds, current 68% / 32%: 8 percentage point drift. Threshold-based rebalancing typically 5% drift triggers action. Under 5%: hold. 10%+ often warrants rebalance — extended drift changes risk profile meaningfully.
Quick example
With current equity of 68% and target equity of 60% (plus rebalance threshold of 5%), the result is 8.00 percentage points. Change any figure and watch the output shift — it's often more useful to see the pattern than to memorise the formula.
Which inputs matter most
You enter Current Equity %, Target Equity %, and Rebalance Threshold. Not every input has equal weight. Adjusting one input at a time toward extreme values shows which ones move the result most.
What's happening under the hood
Standard drift calculation. The formula is listed in full below. If the number looks off, you can retrace the calculation by hand — that's the point of showing the working.
Why investors run this
Most people's intuition for compounding is wrong — not because the math is hard, but because linear thinking doesn't account for curves. Running numbers through a calculator like this one is the cheapest way to recalibrate that intuition before making an irreversible decision about contribution rate, asset mix, or retirement age.
What this doesn't capture
Steady-rate math ignores real-world volatility. Actual returns are lumpy; sequence-of-returns risk matters most in drawdown; fees and taxes drag on compound growth; and behaviour changes in drawdowns can reduce outcomes below the projection. The number represents one scenario rather than a forecast.
Where to go next
This calculation rarely sits alone in a planning exercise. If you're running these numbers, you'll probably also want the portfolio rebalancing calculator, the portfolio rebalancing frequency calculator, and the digital asset portfolio calculator — each one answers a different question in the same territory. Treating them as a set rather than in isolation usually produces a more honest picture.
Your portfolio has drifted 8.00 percentage points from the target allocation of 60, currently at 68.
Inputs
This example uses typical values for illustration. Adjust the inputs above to match a specific situation and see how the result changes.
Sources & Methodology
Methodology
The calculator computes allocation drift by taking the absolute difference between your current equity allocation percentage and your target allocation percentage. It then compares this drift value against your specified rebalance threshold. If the drift exceeds the threshold, the calculator flags that rebalancing may be warranted. The model assumes allocations remain static between review periods and does not account for transaction costs, tax implications, or the timing of market movements. It treats drift as a simple point-in-time measure and does not model the impact of repeated rebalancing on long-term returns or portfolio volatility. This calculation is a straightforward monitoring tool to identify when portfolio composition has drifted from its intended targets.
References
Frequently Asked Questions
Typical threshold?
Tax-efficient rebalance?
Volatile drift?
Age-based shift?
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